Technology of phase change random access memory (PCRAM) is developed from a conception proposed by S. R. Ovshinsky at the end of 1960s that phase change thin film can find applications in phase change storage media. As a recently-emerged non-volatile memory technology, phase change memory (PCM) has advantages over flash memory in many aspects, including read/write speed, read/write times, data retention time, cell area, multiple values, etc. Currently, PCM has become a research focus in the non-volatile memory technology.
A PCM value can be changed by heat treatment of a data-stored phase change layer in a PCM. Phase change materials constituting the phase change layer can be changed into a crystalline state or an amorphous state due to the heating effect by an applied electric current. When the phase change layer is in a crystalline state, PCRAM has a low electrical resistance and the value of memory is assigned to be 0. When the phase change layer is in an amorphous state, PCRAM has a high electrical resistance and the value of memory is assigned to be 1. Hence, PCRAM is a non-volatile memory that can write/read data through an electrical resistance difference of the phase change layer in a crystalline state or an amorphous state.
Conventionally, a bottom contact electrode having a small size can usually be placed between a lower electrode of PCM and the phase change layer to enhance efficiency of PCM. However, the fabrication processes for a conventional PCM are complicated and costly.